1. Field
The present disclosure of inventive concept(s) relates to a method of calibrating a plurality of display panels on a mass production basis, a method of mass producing calibrated ones of such display panels, and a calibration apparatus for performing the methods. More particularly, exemplary embodiments in accordance with the present inventive concept(s) relate to a method of calibrating each of a plurality of mass produced display panels while substantially decreasing an amount of time consumed for taking measurements for each individual one of the mass produced display panels while still achieving a desired degree of accurate calibration and to a calibration apparatus for performing the faster measurement takings.
2. Description of Related Technology
Generally, a liquid crystal display (“LCD”) apparatus includes a first substrate including a plurality of pixel electrodes, a spaced apart second substrate which often includes a common electrode provided thereon and color filters corresponding to primary colors, where a liquid crystal layer is disposed between the first and second substrates. The primary colors may be mixed to produce a desired white (having a respective optical “temperature”). In the LCD, an electric field is generated by voltages applied to the pixel electrode and the common electrode. By adjusting an intensity of the electric field, a transmittance of a light passing through the liquid crystal layer for each primary color may be adjusted so that a desired color image may be formed and displayed.
The LCD display apparatus includes display control circuitry for controlling it so as to display an image corresponding to input image data. To improve reliability of the correspondence between the displayed image and the input image data, typically the whole of the display panel is calibrated by programming it with one or more gamma values and one or more color coordinate mapping values (gamut mappings). For sake of accuracy; it may be desirable to perform gamma calibration and gamut mapping for each of all the possible grayscale values (for example 0-255) and for each subarea of the whole display area (DA) so as to thereby produce a uniformly consistent image for all possible grayscale values and across the whole of the display area of the display apparatus.
More specifically, the gamma value(s) and the color coordinate re-mapping value(s) assigned to each individual display panel may be used to compensate for variations among mass produced display apparatuses coming down an assembly line. The appropriate gamma values and color coordinate values may be extracted for example, by taking measurements at all sub-areas of the full display area (DA) by using all the possible grayscales for each such sub-area. However, this can be too time consuming. For example, when the input image data can have a maximum of 256 different grayscales (GS=0-255) and each measurements taking (e.g., exposure to a measurements taking camera) consumes a finite amount of time, the total time for merely measuring each of the plural display panels in a mass produced steam of such panels can be quite considerable. Subsampling has been proposed to reduce the per panel measurements taking time. Under one subsampling approach, the number of measurements taking exposures has been reduced, but to no less than 10% of the maximum. More specifically, gamma values and color coordinate values of 25 different grayscales are taken on a full screen-per-grayscale bases and then interpolation is used for calibrating the gamma values and the color coordinate re-mappings of all 256 of different grayscales of the display panel.
However, even when snapshot images of 25 sample and full screen grayscales are taken under the 10% subsampling approach and while using an appropriate camera apparatus, a time duration of about 200 ms may be needed for the full screen camera exposure for each one sample grayscale image and an additional 300 ms is needed for serially transmitting the measured data to an appropriate data processing means, where the data is first tested for integrity before the next display panel on the assembly line is allowed to come in front of the camera. Therefore, a minimum time of about 500 ms may be needed for each full screen snapshot and a total time of about 12.5 s (seconds) may be needed for taking the calibration measurements of each single display panel in a mass produced stream of such display panels so that appropriate gamma values and the color coordinate re-mappings values may be programmed into each. This can disadvantageously slow production and increase manufacturing costs. (In a variation, the amount of desired exposure time may vary as a function of the grayscale under measurement, with the darker or lower grayscale values (e.g., closer to GS=0) calling for longer exposure durations and the brighter or higher valued grayscales (e.g., closer to GS=255) calling for comparatively shorter exposure durations.)
As explained above, quite a lot of time may be needed for measurements taking steps during the calibrating of the gamma values and of the color coordinate re-mapping values of each of mass produced display panels. In addition, when all of the display panels of a mass production batch are not individually calibrated due to limits on time availability, the, reliability of the luminance and color balance characteristics of the display panels produced from the batch may decrease. In order for the manufacturer to maintain a reputation of excellent reliability for each display panel in a batch of mass produced and sold display panels, it is desirable that every display panel be individually tested and calibrated rather than relying on batch statistics and hoping that sporadic testing is good enough. On the other hand, it is also desirable for the cost of producing a batch of individually calibrated display panels to be low so that the manufacturer can pass at least part of the cost saving to consumers. The problem is how to achieve both of reduced measurements taking/gathering time and of obtaining a sufficient number of samples in a subsampling process.
It is to be understood that this background of the technology section is intended to provide useful background for understanding the here disclosed technology and as such, the technology background section may include ideas, concepts or recognitions that were not part of what was known or appreciated by those skilled in the pertinent art prior to corresponding invention dates of subject matter disclosed herein.